They Get Questions
The Las Vegas Review Journal takes questions from their readers about cactus. Good deal all around.
What is wrong with them? Do they have a fungus? Also, I forgot what kind of cactus they are.
A: Your cacti do look pretty bad. All of the pads are shriveled like flattened raisins. Cacti like this are usually suffering from water stress: not applying water often enough.
It also can be a sign of root or pad rot developing below ground. Keeping a soil too moist can rot roots and the pad below ground. That, too, is water stress since there are not enough roots for the cactus to bring water to the pads.
These problems are remedied by making sure the soil you use drains easily after irrigating and scheduling your irrigations less frequently.
If the pads and roots appear to be healthy, then the plants are, most likely, not getting watered often enough. Water plants in the ground less often than the same plants growing in containers. The smaller the container, the more often you will need to water. If those same plants were in small containers like yours, I would be watering them every couple of days.
Now, there’s a lot more if you follow the link. It’s quite the extensive discussion of water stress in cacti in Nevada.